A graphical front end for a mailing list tool could be attractive. In
fact, L-Soft, the vendors of LISTSERV (TM), were exploring a GUI client
for LISTSERV as of a couple of years ago. A GUI would be especially
helpful for skimming archives, not just subscribing & posting messages.
However, in my opinion if you want to build a window from the Web into
mailing lists it'd be better to roll a forms-based gateway service than
to add functionality for this to HTML.
One issue is using an installed Web browser package for individual,
specific user applications when in in many cases the software was
installed assuming a mix of anonymous users. In university microlabs
Netscape unfortunately often serves as a fast path to e-mail spoofing,
sometimes accidental, sometimes deliberate. The "mailto:" URL and
proposed cousins assume that each Web browser installed has been
configured for one human to use. That's often not the case.
/rich